The present invention relates to improvements in portable combustion-powered tools, also called powder-actuated tools because of the use of combustible powder charges, and specifically to such a tool having a resetting mechanism that automatically resets the device to the pre-firing configuration and a device for advancing the charges.
Portable combustion-powered tools for use in driving fasteners into workpieces are known and described in the literature. Generally, such devices have the outward geometry of a pistol or gun with a combustion chamber, an explosive charge in the chamber, a fastener that is to be driven when the charge explodes, a piston separating the charge from the fastener, and a handle or grip with a trigger for actuating explosion of the charge.
Upon the pulling of a trigger switch, ignition of a charge creates gas in the combustion chamber, which pushes the piston so as to impact the positioned fastener and drive it into the workpiece. The piston is returned to its original or xe2x80x9creadyxe2x80x9d position by manually resetting the piston and chamber. Fasteners are positioned in a nosepiece where they are held in a properly positioned orientation for receiving the impact of the piston.
In use, the more fasteners that can be driven in a given time usually means that the construction will progress faster to completion. Powder activated technology (PAT) tools typically have a safety mechanism to assure that the device is firmly abutting the surface into which the fastener is to be driven because of the danger of firing the fastener like a bullet; these safeties prevent firing the device except under certain circumstances. However, on these devices the chamber by which the fastener is driven must be reset, and on such devices the reset is performed manually. Although manually resetting can require only a few seconds, it interrupts the fluidity of the construction process. If manual resetting were to be replaced by an automated resetting, the time for driving the fasteners can be significantly reduced.
Analogous devices that are hydraulically or pneumatically operated incorporate automatic reset mechanisms that utilize the same hydraulic or pneumatic pressure that drives the fastener to reset the device. Unfortunately, there is a need for an analogous mechanism for powder-actuated technology tools. Typically, PAT tools are reset manually by grasping the nose of the device where the fastener is loaded and pulling it away from the chamber (i.e., lengthening the device) to reset the piston; for devices in which the charge is provided as a magazine (e.g., an auto-loading strip of charges), this manual reset also advances the magazine.
In addition, the charges in such powder-actuated devices are typically secured or integrated onto a strip, similar to a belt of bullets for a machine gun, but stiffer. The strip with charges is advanced by a lever mechanism that engages the strip on one end and the piston (or a piston guide or similar structure) on the other end. The mechanism for advancing the strip of charges typically includes a lever that not only pivots about a point, but often wobbles about the pivot. This wobble, or misalignment, can cause the mechanism advancing the strip to fail to advance the strip and, sometimes, actually causes the strip to move in the wrong direction, thus disposing a used charge where a fresh charge should be disposed.
One object of this invention is to provide a portable powder-actuated tool that resets automatically after the fastener is driven. The automatic resetting preferrably resets the chamber, and loads another charge from a magazine. In other embodiments, a magazine of fasteners is also provided and the automatic resetting also loads another fastener from the magazine.
In summary, the device comprises a housing having a bore through a longitudinal axis with an open end, piston disposed in the bore, an annular liner having a longitudinal axis coextensive with that of the bore in the housing and engaging the housing where the bore opens, a nose attached to the liner for accepting and retaining a fastener to be driving by the piston, a stop for limiting movement of the piston towards the open end of the bore in the housing, and a spring biasing the housing and nose apart along their coextensive longitudinal axes.
In operation, when the device is charged and in the xe2x80x9creadyxe2x80x9d position with a charge in the chamber and a fastener in the nose, the operator uses the device to press on the object to be fastened so that the spring is compressed. The energy imparted to the spring in compressing it is recovered by having this potential energy converted to kinetic energy to effect a resetting of the device. When the charge is ignited, the piston moves towards the nose and impacts the fastener, forcing it into the object to be fastened. As the operator lifts the device away from the object just fastened, to position the device for the next fastening operation, the force on the spring is released, allowing the stored energy in the spring to urge the nose/liner away from the piston and thereby reset the device. Preferably, the magazine of charges is advanced to load a new charge into the chamber for driving the next fastener.
Also in view of the foregoing, another object of this invention is to provide an improved device and method for advancing the strip of charges in a combustion-powered tool. More particularly, an object of this invention is to provide such an improved device and method that does not misalign and fail to advance the strip. Another object of the invention is to provide a combustion-activated tool having this improved device.
This invention provides a combustion-activated tool comprising (i) a housing having a longitudinal bore that extends to and connects with a vertical bore, (ii) a piston and piston guide disposed within the longitudinal bore and moveable axially therein, and (iii) an advance lever having a reset end and an advancing end, said lever disposed on a pivot skew to the axis of the longitudinal bore, the lever having an axis essentially parallel with the longitudinal bore, the advancing end of the lever attached on an arm of the lever angled to one side of the axis of the longitudinal bore and effective to engage teeth on the side of a strip of charges disposed in the vertical bore, the reset end of the lever being disposed on the same side of the axis of the longitudinal bore and engaging the piston guide.
In summary, the lever for advancing the strip of charges has one end that engages the piston guide and another than engages teeth or recesses on the strip of charges. The longitudinal and vertical bores are orthogonal to each other. Each of the charges on the strip is thus positioned, sequentially, at the intersection of the two bores. The advancing end of the lever is disposed to one side of the strip to engage the teeth thereon, and the reset end of the lever being disposed on the same side but at the position of the piston guide.